HDD Regenerator is commercial software . It typically offers a trial version that allows you to scan the drive and see if bad sectors exist. However, the trial version generally limits the number of sectors it will actually repair (often just the first one or a small batch) to prove the software works.
The legitimate, paid version of HDD Regenerator 1.71 originally cost around $79.99 USD. A valid serial number was a 24-character alphanumeric string (e.g., XXXXX-XXXXX-XXXXX-XXXXX ). When entered into the software, it unlocked: hdd regenerator 171 work full name serial number